Anti-friction bearing grease and preparation thereof



United States Patent f ANTI-FRICTION BEARING GREASE AND PREPARATION THEREOF Arnold J. Morway, 'Clarktownship, N. J., 'assignor' to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application September 30, 1953 Serial No. 383,393

7 Claims. (Cl. 252-331) The present invention relates to improved lubricating greases. and a process for their preparation. More particularly the. invention relates to anti-friction bearing greases useful for high temperatureservice and containing a complex-type soapthickener dispersed in a combination of. high. and low viscosity mineral oils of lubricating. grade.

'.In its broadest aspect the invention pertains to high temperature bearing greases prepared by the formation of. the grease in a low viscosity, low viscosity index lubricating oil and improved with respect to lubrication lifeby the addition of a minor proportion of a high viscosity, high viscosity index oil followed by homogenization at high rates of shear.

In certain lubricating systems, for example those employed for the lubrication of ball bearings and other anti-friction bearings a channeling type grease is required. These greases must provide a low torque and low temperature rise in the bearing. Their consistency should be such that the bulk of the grease is quickly pushed out ofthe path of the rolling elements and remains out of this path during operation of the bearing. The grease must have excellent high and low temperature properties 7 and a long high temperature lubrication life which makes frequent repacking unnecessary.

It is well known in the art that the so-called complex soap-type greases comply best with these requirements. Such greases are thickened with a soap-type grease thickener which in addition to an alkali or alkaline earth metal soap of a high molecular weight soap-forming carboxylic acid contains combined therewith a salt of a a similar metal with a low molecular weight carboxylic acid. An excellent channeling type grease of this general type is described in U. S. Patent No. 2,265,791, issued December 9, 1941, to Zimmer and Morway. The grease of this patent isprepared by a high temperature reaction ofrapeseed oil withalkali hydroxide in lubricating oil.

Quite generally, the channeling characteristics and the lubrication life of these greases are a function of the soap content, i. e. the higher the soap content (within practical limits) the better the channeling quality and the longer the lubrication life of the grease. All these .greases have, therefore, a relatively high soap content.

ished grease with a low viscosity, high viscosity index lubricating oil followed by homogenization of the grease at high rates of shear. A procedure of this type is described in the Morway et a1. application Serial No. 285,712, filed May 5,1952, now United States Patent No.

2,745,810, and assigned to the assigneeof the present application. Others have proposed the use of mixtures of low viscosity lubricating oils with high viscosity low vis- Cir Patented Feb. 3, 1959 cosity index lubricating oils in the grease cooking stage. Whle greases of these types, particularly those described in said application Serial No. 285,712 have excellent channeling characteristics and improved lubrication life, it has not been possible heretofore to prepare channeling greases having a lubrication life substantially in excess of 1600 hours (as measured by the AFBMA-NLGI spindle test) at a soap content of less than 20 wt. percent.

It has now been found that channeling greases complying with all the above mentioned requirements and having a drastically improved lubrication life at relatively low soap contents are obtained'by preparing a channeling type grease in a low viscosity, low viscosity index lubricating oil, blending the finished grease with a lubricating oil of high viscosity and high viscosity index and homogenizing the blended grease at high rates of shear. The high viscosity, high viscosity index oil is preferably used in minor proportions compared to the total amount of oil employed. Proportions of about 5-20 Wt..per-

cent based on total grease are generally suitable. In

.roller bearings, however, severe channeling with accompanying hardening is undesirable and a softer grease less susceptible to shear hardening is desirable. This is accomplished by plasticizing the product with a high viscosity high V. l. residuum while maintaining the soap content at a level high enough to afford long lubrication life. This high viscosity high V. i. residuum apparently prevents thixotropic recovery under high shearing stresses to the same degree as the lower viscosity oils, particularly the low viscosity low V. 1. oil. However, the high viscosity, high viscosity index residuum affords a substantial lengthening of lubrication life far beyond anything predictable from the soap content of the grease. Neither low viscosity, low viscosity index oils, nor low viscosity, high viscosity index oils have this capacity. When it is desired to increase channeling the soap content may be correspondingly increased. From the point of view of lubrication life it would be desirable to use high viscosity index oils as the sole dispersant. However, soaps are not suficiently soluble in such oils to permit the preparation of satisfactory greases.

More specifically, the low viscosity, low viscosity index oil used in the preparation of the channeling grease base should be a distillate oil having a viscosity of about 200-500 S. S. U. at 100 F, a viscosity index of about 40-70 V. I. and a flash point of about 300400 F. Acid refined Coastal oil distillate stocks and others are suitable for this purpose. The oil normally represents about 20-40 wt. percent of the total blended grease.

The high viscosity, high viscosity index oil of the invention should have a viscosity of about 2000-5000 S. S. U at 100 F., a viscosity index in excess of V. I. preferably of 90-120 V. I. and a flash point in excess of about 450 F. preferably about 500-600 F. An oil having these characteristics is best prepared from highly refined, propane deasphalted residues of parafiinic or mixed base crudes such as Mid-Continent or Pennsylvania type crudes.

The low viscosity, high viscosity index oil which may be used together with the high viscosity, high viscosity index oil may have a viscosity of about 350-450 S. S. U. at F., a viscosity index of about 100-120 V. I. and a flash point of about 100-450 F. Highly refined dis- V a tillate oils of Mid-Continent or Pennsylvania origin may be used for the purpose. This oil may be present in the total blended grease in amounts of about 30-50 wt. percent. I

As pointed out above, complex-type soaps are the grease thickeners best suited for the purposes of the present invention. Such complexes may be formed from the metal soaps of high molecular weight soap-forming carboxylic acids having 12-30 carbon atoms and metal salts of low molecular weight carboxylic acids having about 1-6 carbon atoms. High molecular Weight acids such as stearic, hydroxy stearic, hydrogenated fish oil or tallow acids, oleic, ricinoleic and similar acids may be used in combination with formic, acetic, lactic and similar low molecular weight acids in mole ratios of about 0.3-3 moles of high to low molecular weight acid. Advantageous'ly the high and low molecular weight acids are coneutralized and heated above their melting point to dehydration in lubricating oil to form the desired soap complex. Temperatures of about 350-500 F. or higher may be used.

Metal bases useful in the preparation of channeling greases include the alkali and alkaline earth metal hydroxides and carbonates. Alkali metal hydroxides and particularly sodium hydroxide are preferred for the pur-' poses of the invention.

The sodium soap of rapeseed oil prepared by alkali fusion of rapeseed oil for example as described in said U. S. Patent 2,265,791, is a complex soap of the type mentioned above and the preferred grease thickener of the invention. This thickener may be prepared by admixing the rapeseed oil with a portion of a mineral base oil of lubricating grade, good soap solvency properties but relatively low viscosity and low viscosity index, adding sodium hydroxide and heating to about 480 to 520 F. or higher until gas evolution is receding. Normally, a small proportion of a petroleum sulfonate is added prior or during the heating stage. Other modifiers such as oxidation inhibitors may be added during or after cooling.

Greases in accordance with the present invention, quite generally, may be made as follows. A grease base stock may be prepared in a low viscosity, low viscosity index oil of the type described above by any of the conventional methods mentioned before. The finished or semi-finished base grease which may contain a high thickener concentration of say about 20-50 wt. percent is then blended with the high viscosity, high viscosity index oil in the desired proportion and the blended grease is subjected to homogenization at high rates of shear of say about 10,000500,000 reciprocal seconds, preferably 100,000 to 400,000, reciprocal seconds. When a low viscosity, high viscosity index cut back oil is used it may be added together With the high viscosity, high viscosity index oil and blended into the grease by homogenization. Equipment suitable for homogenization includes the Gaulin homogenizer, rolling mills having steel rollers with minute clearances, the Moorehouse mill, pressure viscosimeters,

or the like. However, homogenizing equipment of the Gaulin type is preferred.

It has also been found that the substantially conventional procedure of the first grease making stage may be advantageously modified by substantially reducing the cooling time. In the prior art it has been the general practice to allow a cooling time of about 24 to 36 hours for the grease to cool from the fusion temperature of say about 500 F. to a packaging temperature of say about 200-275 F. This technique results in uneconomical equipmnet tie-up. The present invention permits cutting of this cooling time to about 210 hours without any disadvantage in grease quality or yield. Rapid cooling of this type may be accomplished by circulating cold water through the jacket of the grease kettle or any other suitable cooling method.

The invention and its advantages will be best understood from the following specific examples.

4 EXAMPLE I A grease base was prepared from the following ingredients.

Ingredients: Percent weight Rapeseed oil 29.00

Vis.

55 S. S. U. 200 F. 500 S. S. U. F. V. I., 40 Flash point, F., 395

Preparation.The rapeseed oil and A of the mineral oil were charged to a fire heated grease kettle and warmed to F. The sodium sulfonate was then added followed by a 40% aqueous solution of the sodium hydroxide. The mass was heated to 350 F., where most of the water was removed. The balance of the mineral oil was added, and the temperature raised to 500 F. At this temperature the heating was discontinued and the hot grease transferred to a cooling kettle and rapidly cooled to 275 F., i. e. below the transition point, within about 4 hours. The inhibitors were added and the grease further cooled to 200 F.

This grease was then blended with an equal weight of a dumbbell blend of solvent refined distillate from a Mid- Continent crude, bright stock and residuum, together with additional inhibitors in the proportions tabulated below.

Finished grease composition Gaulin homogenizer and homogenized to its ultimate hardness. The resultant product was of excellent structure and homogeneity.

Properties of finished grease.-Appearance-excellent,

smooth, homogeneous, short fiber product.

Penetrations 77 F. mm./10:

Unworked 340 Worked 60 strokes 342 Worked 100,000 strok (270 t hole worker plate) 420 101120910 stroke worked grease rehomogene Worked 60 strokes 347 Dropping Point, "F 481 Percent Free Alkalinity as N aOH 0.1 Percent Separation, 50 hours at 150 F.,

60 mesh cone test 0.8

Norma-Hoflmann Oxidation:

Oz pressure drop 5 10 15 20 Hours 158 254 318 342 AFBMA-NLGl Spindle Testz 250 F.10,000 R. P. M. Hours 4, 606

1 Operating conditions: 22 hours at 250 F.; 2 hours shut down and cooled to room temperature, 5 days a week; run straight through weekends on temperature 250 F.

In the manufacture of the grease of the invention, the rapeseed 011 soap was dispersed with heating in the relatively polar coastal distillate. In less. polar type oils, such as the solvent refined oil-residuum. blend thesoap will riot give a satisfactory structure, Therefore the soap concentrate must be dispersed by mechanical means rather than heat after formation of the base grease. With present equipment, up to 50% soap can be incorporated in the base grease, and this product then mechanically blended with the solvent refined stocks by homogenizationas shown in Example 1.

EXAMPLE II Six difierent greases A, B, C, D, E; and F wereprepared as follows.

Grease A was substantially identical with the base grease of Example I and prepared in the same manner. That is, it was not blended with additional oil after cooling.

Grease B was a similar base grease containing a slight- 1y lower soap content and an oil of lower viscosity.

Greases C and D were prepared as grease B followed by cutting back with the same oil and homogenizing to obtain similar consistencies but lower soap content.

Grease E was prepared as grease B followed by cutting back with a blend of low viscosity, high viscosity index oil and a small amount of bright stock residuum and homogenizing.

Grease F was prepared in accordance with the invention by cutting back grease A with the cut back of grease E plus a high viscosity, high viscosity index oil U LUBRICATION LIFE [AFBMA-NLGI spindle tests (10,000 R. P. M. and 250 F.).]

Soap SSU Vis./ Lubrica- Grease Con- Mineral Oil Constituent 100 F. of tion tent Mineral Life,

Oil Hours 30 Distillate from Coastal Crude 500 1, 200 25 d 300 1, 600 18 do 300 1,000 12 d0 300 700 44g, 1S)ilst. fiaofil goagtlanligrtlrged 52 0 o ven e ne i 12 Continent Crude 3 330 800 4% Bright Stock 4 36% Dist. from Coastal Crude 34%;I jbzlogrengRefitngd from 1 on men ru e F 11% Dewaxed and Deasphalted 500 606 Mid-Continent Residuum- 4% Bright Stock 4 Gravity, Flash, SSU Pour, A. P. I. O. C., Vis./ V. I F.

It will be noted that the lubrication life of the grease of the invention (grease F) is almost three times that of the best known grease (grease E) without an appreciable increase in soap content. The superiority of grease F over greases A, B, C and D most of which contain substantially more soap but no high viscosity, high viscosity index oil is even more striking.

Recently it has been found that greases giving long lubrication life in pre-packed anti-friction ball bearings, when containing sufiicient soap to form desirable channeling type greases, tend to impart high frequency whine to an operating bearing. Lowering the soap content of these type greases apparently softens the products sufiiciently to prevent noise. However, due to internal friction developed in the hearing by the-churning of the softer greasejhigh bearing temperatures result with accompanying high po'wer consumption. This is undesirable since it leads to earlybreakdown ofthe grease with resultant bearing failure;

T he grease of the invention (grease F) prevents this noisy bearing operation but tends to give a slightly higher heating temperature rise than is desirable in pre-packed large size bearings. In other type bearings (e. g. roller bearings)" the grease is entirely satisfactory. By increasing the soap'content to 25 to 27% extremely long bearing life is obtained with freedom from noise and extremely low temperature bearing operation accompanied by a low power requirement.

To summarize briefly, the essential element of the present invention resides in the presence of a high viscosity, high viscosity index oil in a channeling type anti-friction bearing grease prepared in a low viscosity, low viscosity index oil. Homogenization of the grease affords excellent grease consistency coupled with the extremely long lubrication life resulting from the addition of the high viscosity, high viscosity index oil.

The invention is not limited to the specific compositions and conditions set forth in the above examples. These may be varied within the ranges disclosed to prepare greases of varying characteristics within the scope of the invention.

What is claimed is:

1. In a process of preparing a grease composition having an AFBMA-NLGI spindle test life in excess of 1600 hours comprising a major proportion of mineral lubricating oils and a minor grease-making proportion of a complex soap-salt thickener of a metal soap of a high molecular weight soap-forming carboxylic acid with a metal salt of a low molecular weight salt-forming carboxylic acid, said metal being selected from the group consisting of alkali metals and alkaline earth metals; the improvement comprising forming said complex soap-salt thickener at a temperature above 350 F. in a first distillate oil having a viscosity in the range of 200 to 500 S. S. U. at 100 F. and a viscosity index in the range of 40 to 70, then adding additional oils thereto, and finally homogenizing the grease at a rate of shear in the range of 10,000 to 500,000 reciprocal seconds, said mineral lubricating oils in the final product comprising in the range of 20 to 40 wt. percent of said first oil, in the range of 5 to 20 wt. percent of a residuum having a viscosity in the range of 2,000 to 5,000 S. S. U. at 100 F., a viscosity index in the range of to 120, and a flash point above 450 F., and in the range of 30 to 50 wt. percent of a second distillate oil having a viscosity in the range of 350 to 450 S. S. U. at F. and a viscosity index in the range of 100 to 120.

2. The process of claim 1 wherein said complex is prepared by reacting rapeseed oil with sodium hydroxide at a temperature in the range of 480-520 F.

3. The process of claim 1 wherein said grease-making proportion is in the range of 25-27 wt. percent on total grease.

4. The process of claim 1 wherein said metal is sodium.

5. The process of claim 1' wherein said high molecular weight carboxylic acid has in the range of 12-30 carbon atoms and said low molecular weight carboxylic acid has in the range of 1-6 carbon atoms.

6. The process of preparing a high temperature grease having long lubrication life in anti-friction bearings which comprises preparing a base grease by heating a mixture of about 29 wt. percent on base grease, of rapeseed oil and about 32 wt. percent, on base grease, of a refined Coastal distillate oil of 500 S. S. U. viscosity at 100 F. and 40 viscosity index to about F., adding about 0.8 wt. percent, on base grease, of sodium petroleum sulfonate, adding about 5.9 wt. percent, on base grease, of sodium hydroxide as a 40% aqueous solution, heating the mass to about 350 F. to dehydrate the same,

adding about 31 wt. percent, on base grease, of said Coastal oil, raising the temperature to about 500 F., rapidly cooling the mass to about 275 F. within about 4 hours, adding about 1.5 wt. percent, on base grease, of inhibitors and further cooling to about 200 F.; blending the base grease so prepared with an about equal weight of a blend of about 8-9 wt. percent, based on total grease, of a solvent refined, propane precipitated Mid-Continent residuum of about 2200 S. S. U. viscosity at 100 F. and about 100 viscosity index with about 3940 wt; percent, based on total grease, of a solvent refined Mid-Continent distillate of about 367 S. S. U. viscosity at 100 F. and about 102 viscosity index; and homogenizing the 7. The grease prepared. by the process of claim 6.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,791 Zimmer'et al. Dec. 9, 1941 2,375,485 Morgan et al. May 8, 1945 2,455,892 Fraser Dec. 7, 1948 2,614,079 Moore Oct. 14, 1952 2,652,365 Moore et a1 Sept. 15, 1953 2,678,918 Bondi May 18, 1954 

6. THE PROCESS OF PREPARING A HIGH TEMPERATURE GREASE HAVING LONG LUBRICATION LIFE IN ANTI-FRICTION BEARINGS WHICH COMPRISES PREPARING A BASE GREASE BY HEATING A MIXTURE OF ABOUT 29 WT. PERCENT ON BASE GREASE, OF RAPESEED OIL AND ABOUT 32 WT. PERCENT ON BASE GREASE, OF A REFINED COASTAL DISTILLATE OIL OF 500 S.S.U. VISCOSITY AT 100* F. AND 40 VISCOSITY INDEX TO ABOUT 150* F., ADDING ABOUT 0.8 WT. PERCENT, ON BASE GREASE, OF SODIUM PETROLEUM SULFONATE, ADDING ABOUT 5.9 WT. PERCENT, ON BASE GREASE, OF SODIUM HYDROXIDE AS A 40% AQUEOUS SOLUTION HEATINGTHE MASS TO ABOUT 350* F. TO DEHYDRATE THE SAME ADDING ABOUT 31 WT. PERCENT ON BASE GREASE, OF SAID COASTAL OIL RAISING THE TEMPERATURE TO ABOUT 500* F., RAPIDLY COOLING THE MASS TO ABOUT 275* F. WITHIN ABOUT 4 HOURS, ADDING 1.5 WT. PERCENT ON BASE GREASE, OF INHIBITORS AND FURTHER COOLING TO ABOUT 200* F., BLENDING THE BASE GREASE SO PREPARED WITH AN ABOUT EQUAL WEIGHT OF A BLEND OF ABOUT 8-9WT. PERCENT, BASED ON TOTAL GREASE, OF A SOLV ENT REFINED, PROPANE PRECIPITATED MID-CONTINENT RESIDUUM OF ABOUT 2200 S.S.U. VISCOSITY AT 100* F. AND ABOUT 100 VISCOSITY INDEX WITH ABOUT 39-40 PERCENT, BASED ON TOTAL GREASE, OF A SOLVENT REFINED MID-CONTINENT DISTILLATE OF ABOUT 367 S.S.U. VISCOSITY AT 100* F. AND ABOUT 102 VISCOSITY INDEX AND HOMOGENIZING THE GREASE SO PREPARED AT HIGH RATES OF SHEAR OF ABOUT 10,000500.000 RECIPROCAL SECONDS. 